Carbonic anhydrases are influenced by the size and symbiont identity of the aggregating sea anemone Anthopleura elegantissima.

Carbonic anhydrases (CA; EC 4.2.1.1) play a vital role in dissolved inorganic carbon (DIC) transport to photosynthetic microalgae residing in symbiotic cnidarians. The temperate sea anemone Anthopleura elegantissima can occur in three symbiotic states: hosting Breviolum muscatinei (brown), hosting Elliptochloris marina (green) or without algal symbionts (aposymbiotic). This provides a basis for A. elegantissima to be a model for detailed studies of the role of CA in DIC transport. This study investigated the effects of symbiosis, body size and light on CA activity and expression, and suggests that A. elegantissima has a heterotrophy-dominated trophic strategy. We identified putative A. elegantissima CA genes and performed phylogenetic analyses to infer subcellular localization in anemones. We performed experiments on field-collected anemones to compare: (1) CA activity and expression from anemones in different symbiotic states, (2) CA activity in brown anemones as a function of size, and (3) CA activity in anemones of different symbiotic states that were exposed to different light intensities. CA activity in brown anemones was highest, whereas activity in green and aposymbiotic anemones was low. Several CAs had expression patterns that mirrored activity, while another had expression that was inversely correlated with activity, suggesting that symbionts may induce different DIC transport pathways. Finally, CA activity was inversely correlated with anemone size. Our results suggest that the observed CA activity and expression patterns are affected not only by symbiosis, but also by other factors in the host physiology, including trophic strategy as it relates to body size and cellular pH homeostasis.

Uptake and partitioning of copper and cadmium in the coral Pocillopora damicornis.

Coral-reef ecosystems are increasingly being impacted by a wide variety of anthropogenic inputs, including heavy metals, which could be contributing to coral reef stress and bleaching episodes. Fragments of Pocillopora damicornis were exposed in the laboratory to cadmium (Cd) or copper (Cu) chlorides (0, 5, 50 microg l(-1)) for 14 days and analyzed for metal content in the whole association, algal or animal fractions. Various physiological and biochemical parameters were also measured, such as, algal cell counts, mitotic index, chlorophyll content and levels of the antioxidant glutathione (GSH). Cd and Cu accumulation were observed at all time points and doses; there was no evidence of differential metal partitioning between the algal or animal fractions. No changes in algal cell density, mitotic index or chlorophyll content from the controls were observed in any of the metal treatments. GSH levels were significantly higher in the 5 microg l(-1) Cd (Day 4) and Cu (Days 4 and 14) treatments compared with controls at the same time point. Although no evidence of a bleaching response occurred, corals in both 50 microg l(-1) metal exposures sloughed off tissues and did not survive the duration of the exposure period. Our results demonstrate the accumulation of Cd and Cu in P. damicornis and mortality in the absence of a bleaching response.

Differential accumulation of heavy metals in the sea anemone Anthopleura elegantissima as a function of symbiotic state.

The accumulation of metals by the North American Pacific Coast temperate sea anemone Anthopleura elegantissima, and its dinoflagellate-algal symbiont Symbiodinium muscatinei was examined following laboratory metal exposures. Both, naturally occurring symbiotic and symbiont-free (aposymbiotic) anemones were used in this study to investigate differences in metal uptake due to the symbiotic state of the animal. The effects of metal exposures on the anemone-algal symbiosis were determined using measures of algal cell density and mitotic index (MI). Anemones were exposed to either cadmium, copper, nickel or zinc chloride (0, 10, 100 microg l(-1) for Cd, Cu and Ni; 0, 100, 1000 microg l(-1) for Zn) for 42 days followed by a 42-day recovery period in ambient seawater. Anemones were analyzed for metal content using inductively coupled plasma mass spectroscopy (ICP-MS) at various time points during the study. Symbiotic anemones accumulated Cd, Ni and Zn to a greater extent than aposymbiotic anemones. A dramatically different pattern of Cu accumulation was observed, with aposymbiotic anemones accumulating higher levels than symbiotic anemones. Following recovery in ambient seawater, all tissue metal levels were reduced to near pre-exposure control levels in most cases. No changes in algal cell density or MI were observed in symbiotic anemone tentacle clips at any dose or time point in the Cd and Cu exposures. However, significant reductions in algal cell densities were observed in the Ni-exposed and some Zn-exposed animals, although levels returned to control values following recovery. There were no changes in mitotic index (MI) following Ni or Zn exposures. These results demonstrate that the extent of heavy metal accumulation depends upon cnidarian symbiotic state and the heavy metal in question.